The invention relates to a method for determining a target steering torque for a steering means of a steering device in a vehicle.
The invention also relates to a controller for controlling a steering device in a vehicle. The invention further relates to a computer program that can be executed on a controller for controlling a steering device in a vehicle.
In modern steering devices, for example in an electric power steering (EPS) system or in what is referred to as a Steer-by-Wire (SbW) steering system, a target steering torque is determined, which is applied to a steering means, such as a steering wheel, in order to counteract the force applied by the driver or support the force applied by the driver. The target steering torque can also be referred to as the target manual torque. This is intended to convey a driving experience to the driver that corresponds to the current driving situation. In a conventional steering system, in which a mechanical connection exists between the steering means and the wheels to be steered, the target steering torque decisively depends on cornering forces that act on the steering device, and ultimately on the steering means, via a steering linkage.
In SbW steering systems, the target steering torque is generated, for example, by means of a suitable steering wheel actuator. In an EPS system, in which a mechanical connection exists between the steering wheel and the wheels to be steered, modern control designs allow a target steering torque that corresponds to the target manual torque to be established so as to generate a desired steering feel at the steering wheel. To this end, an electric motor, or an electromechanical servo unit, is actuated or adjusted so that the target steering torque is set in accordance with the desired target manual torque. The target steering torque can specify the torque at the torsion bar, or the torque at the steering wheel.
Various approaches exist for calculating the target manual torque, or for calculating the target steering torque, for both SbW systems and for EPS systems having a control design for controlling the steering torque. Depending on the type of the steering system, the steering torque corresponds, for example, to the manual torque and/or to what is referred to as the torsion bar torque. The aforementioned approaches are based on various application functions; however, when combined, they do not convey a satisfactory steering feel in some driving conditions, or in some driving situations. For example, the current transverse acceleration, in the form of the toothed rack force, can be taken into consideration in determining the target steering torque. In addition, further variables may be included. Moreover, existing application functions can be included, which take into consideration, for example, additional moments of friction, so that the effect of the transverse acceleration actually experienced at the steering means can be represented more realistically.
In principle, determining the target steering torque first entails the problem of selecting suitable input variables. These input variables can then be combined in a variety of ways, such that the influence of an individual input variable is frequently no longer fully traceable, and thus it is difficult to correct or improve the target steering torque.